Instruments are used in industrial applications to control processes. For example, flow meters are used to measure the mass flow rate, density, and other characteristics of materials flowing through a pipeline. The flowing materials can comprise liquids, gases, combined liquids and gases, solids suspended in liquids, liquids including gases and suspended solids, etc. The flow meter can be used to measure a flow rate (i.e., by measuring a mass flow through the flow meter), and can further be used to determine the relative proportions of components in a flow stream. The flow meter can provide data of the measurements through, for example, an interface that is accessible by an operator. Using the data provided by the flow meter, other instruments such as valves and pumps can control the materials flowing through the pipeline.
The flow meter can be employed in a wide range of industrial applications. As a result, the flow meter is often required to meet a wide range of environmental specifications. For example, the flow meter may be required to reliably function in high humidity while being subjected to temperature cycles or corrosive environments. The flow meter might also be required to accept data input in these environments. That is, an operator working on the pipeline may be required to input data into the flow meter under various environmental conditions. To input the data, the operator typically presses buttons on an interface. Due to the environmental conditions, the buttons in prior art interfaces can be prone to performance issues. For example, mechanical buttons can be subjected to corrosion in high humidity environments. Infrared buttons might need calibration routines to operate reliably in both high and low temperature. As a result, the data input through prior art buttons can include errors.
Although the interface could be configured for specific environments, such special configurations are cost prohibitive and can be the source of additional defects. Accordingly, there is a need for touch sensors that reliably operate in a wide range of environmental conditions.